Soundproofing: 1/2 inch vs. 5/8 inch drywall - AVS Forum
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post #1 of 58 Old 03-18-2010, 11:36 AM - Thread Starter
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I'm in the process of framing my HT build and I am not planning on doing extensive soundproofing. One layer of drywall, no RISC clips or hat channels, no DD/GG, but I *am* going to install a drywall ceiling and also decouple my walls and use a staggered stud arrangement on wall between the HT and the adjacent room. It's not that I don't CARE about soundproofing, but I'm just not able to go all-out with all the extras that many of you guys use for your dedicated HT rooms. So, I'm using good soundproofing practices where I can: solid entry door, decoupled walls, insulation in ceiling and walls, no ceiling can lighting, etc.

That being said, I was originally planning to use 5/8" drywall, but it occurs to me that I might be able to get away with 1/2" drywall instead. Without only one layer of drywall, is the mass-benefit of the 5/8" worth the extra cost and physical effort of installing it? I'm going to do the work myself, so if I can install 50 lb. slabs of 1/2" drywall instead of 70 lb. slabs of 5/8", I'd do it if it made no noticeable difference in soundproofing quality.

I'm not looking for a night-and-day difference, but if it will make a NOTICEABLE difference, then I'd go for the 5/8". Maybe one of you more experienced guys can tell me if the 1/2" drywall would be "just as good" in this particular application.

--Drew


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post #2 of 58 Old 03-18-2010, 11:47 AM
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Go 5/8 for the mass and the rigidity of the wall board...
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post #3 of 58 Old 03-18-2010, 01:15 PM
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What is your stud spacing? A quick Google search shows that if you are using 24inch on-center studs you'll want to use at least 5/8" drywall to avoid "waves" in the finished wall and ceiling.

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post #4 of 58 Old 03-18-2010, 02:09 PM - Thread Starter
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16" O.C. stud spacing everywhere, including the ceiling and soffit supports.

The "waves" in the wall is an interesting perspective. I have waves all over the rest of my house. I suspect that with my black painted ceiling in the HT, that won't be a problem, but the walls will be a burgundy color, so that might be a consideration. However, I do have columns on the side walls so that the longest span is only about 6 feet or so, so it's unlikely I'd see any waviness anyways.

But thanks for the thought.

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post #5 of 58 Old 03-18-2010, 02:17 PM
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Given you have taken nearly every other step towards soundproofing except for adding the DD mass, why not reconsider things and spend the few extra dollars for two layers of 5/8" drywall? Price it out, I suspect it won't be a deal breaker.

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post #6 of 58 Old 03-18-2010, 03:24 PM - Thread Starter
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Quote:
Originally Posted by Cathan View Post

Given you have taken nearly every other step towards soundproofing except for adding the DD mass, why not reconsider things and spend the few extra dollars for two layers of 5/8" drywall? Price it out, I suspect it won't be a deal breaker.


It's a few hundred dollars more, maybe $300 or $400 with the GG. I guess I figured with the non-hat-channel ceiling and adjoining "open" equipment closet (only covered with an acoustic panel and a foam rubber door seal), going DD/GG on the walls/ceiling wouldn't help that much. I guess maybe I should read more about it. But it seems that most people who go with the DD/GG are going ALL the way with soundproofing. I'm just not sure how much that would add without decoupling the ceiling as well.

Granted, it's not THAT expensive to do, but it's more than double the drywall work and I'd just want to make sure that the benefit was worth the effort.

Besides, from what I understand, you'd want one layer of 5/8" and one layer of 1/2" drywall with the GG in between instead of two 5/8" layers. But otherwise, I get your point. Maybe one of the experts will chime in.

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post #7 of 58 Old 03-18-2010, 03:47 PM
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I did my ceiling with two layers of 1/2' and r19 above it. No gg, clips, channel, or decoupling. Lfe leaks through it like nothing is there. High frequencies are blocked very well. You can talk very loudly and not hear much at all. I have a very loud compressor and I could barely hear it in the bedroom above me. I cant see a little extra drywall making a noticeable difference, but I can only comment on using 1/2".
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post #8 of 58 Old 03-18-2010, 07:02 PM
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You want two layers of 5/8ths if you use GG. The dampening is enhanced by constraining layers having equal stiffness. The differing widths was for non GG assemblies.

You can get 70% of the GG benefit with 50% coverage if budget is an issue, but you'd need to find a way to address the EQ rack IMHO. RSIC-V clips are also less than 50% of whisper or RSIC-01 clips, if you chose to do the ceiling right also, with a slight dip in performance.
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post #9 of 58 Old 03-18-2010, 09:20 PM
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Quote:
Originally Posted by dc_pilgrim View Post

You want two layers of 5/8ths if you use GG. The dampening is enhanced by constraining layers having equal stiffness. The differing widths was for non GG assemblies.

You can get 70% of the GG benefit with 50% coverage if budget is an issue, but you'd need to find a way to address the EQ rack IMHO. RSIC-V clips are also less than 50% of whisper or RSIC-01 clips, if you chose to do the ceiling right also, with a slight dip in performance.

Can you elaborate why different widths of drywall is better for non GG assemblies? I'm also thinking of using two layers of 1/2 inch drywall for the ceiling but without GG, so I'm curious if using 5/8" and a 1/2" drywall would add much benefit.

Instead of using clips, Ted White recommended that you could attach the hat channels directly onto the joists. Clips would be better, of course, but this might work if budget is an issue.
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post #10 of 58 Old 03-18-2010, 09:20 PM
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Drew - I was going to just treat my one wall between the HT and the adjacent room like you are planning. The feedback I got on this forum was that if I wasn't going to treat the others, then I was just wasting my time on the one wall.

I plunged in and did staggered studs all around, DD/GG is planned for the walls and ceiling. I also added another layer of subfloor with GG.

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post #11 of 58 Old 03-19-2010, 02:32 AM
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Quote:
Originally Posted by lpw View Post

Can you elaborate why different widths of drywall is better for non GG assemblies? I'm also thinking of using two layers of 1/2 inch drywall for the ceiling but without GG, so I'm curious if using 5/8" and a 1/2" drywall would add much benefit.

The idea was that there was different resonance points in the two different layers, and that would enhance the isolation benefits. I am not sure if that was conclusively determined to be better than more mass. But you see the idea pop up here every now and again, and in GG approaches the answer is clear.
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post #12 of 58 Old 03-19-2010, 07:06 AM
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Mixing thicknesses of drywall to control resonance was common years ago before semi-liquid damping compounds and constrained layer damping came along.

Now we strive for more mass, and keep the layers similar. So double or triple 5/8" becomes the standard.

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post #13 of 58 Old 03-19-2010, 08:11 AM - Thread Starter
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Quote:
Originally Posted by Ted White View Post

Mixing thicknesses of drywall to control resonance was common years ago before semi-liquid damping compounds and constrained layer damping came along.

Now we strive for more mass, and keep the layers similar. So double or triple 5/8" becomes the standard.


Thanks for weighing in, Ted. But you have no other comments regarding the efficacy of using a 1/2" vs. 5/8" single drywall layer? I was sure you'd have some theory to share!

Obviously, the decoupled ceiling with DD/GG solution is preferred, but is there no benefit in using 5/8" vs. 1/2" with a single layer?

--Drew


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post #14 of 58 Old 03-19-2010, 08:26 AM
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Mass is king. So 5/8" is better than 1/2". Nearly the same price in most locations.

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post #15 of 58 Old 03-19-2010, 08:33 AM
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Why not add this to the mix Quiet Rock?

From 1/2 residential to 1-3/8 THX professional products, QuietRock sound damping drywall hangs and finishes just like standard drywall. Fully lab and field tested to STC 80 (depending on model and assembly).* <--- of course
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post #16 of 58 Old 03-19-2010, 08:47 AM
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With drywall, there really are few scenarios where a field application of damping compound and board isn't a much better option. Field application yields higher mass, higher damping, lower cost, less expensive waste and overlapping seams.

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post #17 of 58 Old 03-19-2010, 11:47 AM
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Quote:
Originally Posted by ithunter View Post

Why not add this to the mix Quiet Rock?

From 1/2 residential to 1-3/8 THX professional products, QuietRock sound damping drywall hangs and finishes just like standard drywall. Fully lab and field tested to STC 80 (depending on model and assembly).* <--- of course

It's way more expensive and more difficult to work with than DD. It does has it's applications, but it's not a price to performance leader.

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post #18 of 58 Old 03-19-2010, 01:26 PM - Thread Starter
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It just occurred to me that I have a soffit that covers about 1/2 of the room (split almost right down the middle lengthwise) that I cannot decouple anyways. The ceiling height is a huge problem and I'm pushing the limits of acceptability as it is, even without reducing it another 2 inches for a hat channel and DD. I have it framed in with 1x4 lumber and will apply the drywall directly to that. Ceiling height will be 7 feet on the nose for the main floor and about 5' 8" above the riser at the back of the room.

So, I guess now the question becomes: will the extra decoupling/DD/GG be effective at all, considering I could only really do it on one side (one half) of the room? Or should I just go with my original plan of putting the 5/8" drywall directly on the ceiling joists and call it a day?

And maybe the last question is: would another layer of 5/8" drywall with GG on the half-ceiling (not the soffit) accomplish anything at all, or is that a waste of time too?

I'll try to post some pictures tonight to make it clearer.

--Drew


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post #19 of 58 Old 03-19-2010, 04:21 PM
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Definitely post some photos of the ceiling/room. It would be helpful to know what the obstruction is and if there is a work around. I posted a good number of photos on how I decoupled my low basement ceiling. Lost only about 1/3" below the joists. I consider sound proofing very important because I wouldn't be able to enjoy the room if my wife was getting pissed because she has to listen to what I'm watching when she isn't in the room.

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post #20 of 58 Old 03-19-2010, 04:44 PM - Thread Starter
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Well, I discussed the soundproofing with my wife before I started the project and she said didn't care if she could hear the HT all over the house! Our walls are pretty thin, so we're used to having TV sounds and kids screaming everywhere. My bigger concern is hearing those TV sounds and kids screaming getting INTO the HT room. It would be tough to tell everyone to be quiet for 3 hours while I watch a movie.

Anyways, pictures will be forthcoming.... I gotta find the camera.

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post #21 of 58 Old 03-19-2010, 05:27 PM
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You have just described the scenario that the experts here preach about. Not only do you want to limit sound leakage out, but possibly more importantly -- in. Dennis has outlined the scenario many times about overcoming the baseline SPL in the room w/o introducing any additional sources.

Think about a movie scene where two individuals are whispering -- then add a 3 year old's play date in the adjoining room.
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post #22 of 58 Old 03-19-2010, 05:53 PM - Thread Starter
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I still have to find the time to set up some sort of online photo hosting account, but for the time being, here are some images of my room.

Pictures are descriptively titled. Note that none of the walls are TRULY decoupled from the ceiling joists, as they are attached directly to them. I did use a staggered stud arrangement on the outward-facing walls. The walls against the foundation/insulation are standard walls.

The soffit was made from 1x4's with a minimum of clearance underneath the HVAC ducts. The reason I didn't use a ladder-style arrangement and just go with drywall underneath is that the span of the two parallel ducts is about 45 inches. There's just no way drywall will accommodate that span by itself. And the gap between the ducts is too small to get anything into.

Anyways, if anyone can suggest any improvements going forward, I would consider them. I don't want to tear down and rebuild, if at all possible.
LL
LL
LL
LL
LL

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post #23 of 58 Old 03-19-2010, 05:54 PM - Thread Starter
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More pictures.
LL
LL

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post #24 of 58 Old 03-19-2010, 05:57 PM
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Will a 1x4 support drywall over 45"?

Is it possible to spread your two ducts slightly so you can put a ladder between them allowing you span them with drywall?
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post #25 of 58 Old 03-19-2010, 06:04 PM
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Quote:
Originally Posted by Stereodude View Post

Will a 1x4 support drywall over 45"?

Is it possible to spread your two ducts slightly so you can put a ladder between them allowing you span them with drywall?

I was wondering the same thing. I don't think that is enough support.

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post #26 of 58 Old 03-19-2010, 06:52 PM - Thread Starter
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Quote:
Originally Posted by Stereodude View Post

Will a 1x4 support drywall over 45"?

Is it possible to spread your two ducts slightly so you can put a ladder between them allowing you span them with drywall?

Quote:
Originally Posted by Big Worms View Post

I was wondering the same thing. I don't think that is enough support.



Oh, yeah, it's strong enough. I weigh around 140 and I could probably hang from two of the parallel 1x4's. They're surprisingly strong and stiff. At 70 lb. per sheet of drywall, each of the three 1x4's in the 4-foot span would have to carry only around 12 lb. each along the entire 45-inch length. Heck, unsupported 5/8" drywall can span up to 23 inches all by itself. So, I think I'm safe.

I suppose in the grand scheme of things, I could have torn down all the ducting and spaced it another inch or so apart so that I could get a ladder in there, but I'm not about to do that now.

--Drew


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post #27 of 58 Old 03-20-2010, 11:20 AM - Thread Starter
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By the way, in the "SS_wall" picture, you can see where there would be a flanking noise path over the top of the wall and the I-beam into the soffit area of the HT from the adjoining room. I'm not sure I can eliminate this, as there is a clear path up above the drop-ceiling in the other room, over the I-beam, and directly into the soffit.

I guess I was hoping to do a DD/GG on the adjoining wall in the OTHER room, as there are fewer obstructions along that wall. This should have the same effect as putting it into the HT room, right?

I was hoping to just pack the soffit with insulation and hope that it would have some muting effect on the noise from the neighboring room.

I'm just not sure what would be effective and what would be a waste of time at this point. But I need to decide SOON because I'm getting ready to do the wiring and the drywalling will be immediately after that.

--Drew


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post #28 of 58 Old 03-20-2010, 12:45 PM
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You can stuff that gap with insulation where possible, any perhaps cut some wood to fit the larger gaps.
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post #29 of 58 Old 03-21-2010, 09:25 AM - Thread Starter
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So I posted pictures and nobody has any suggestions?

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post #30 of 58 Old 03-22-2010, 02:33 PM - Thread Starter
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I guess this is why I don't really post too many difficult questions here.

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